Because there are very few train describers in which output to the Network Rail TD feed. Inverness Highland Workstation is the only one.
As Highlandspring says, we just don't get data for these areas, except for the Inverness centre, which covers about a third of the HML north of Perth and a chunk of the Aberdeen-Inverness line, which are mapped on Traksy.
We'd like to map more of it on Traksy, but the best we can do at the moment is something in the style of West Highland line or Worcester, where we populate berths based on the manual reports. As it stands this is only marginally better than nothing and is time-consuming to build, so it's not too high on the queue.